Disposable diapers provide substantial advantages and convenience over diapers intended to be laundered and reused, and in recent years disposable diapers have met with increased success in the marketplace. Typical disposable diaper structures include a moisture retaining layer of relatively high liquid holding capacity sandwiched between a moisture pervious facing layer to be directed against the infant's skin, and a moisture impervious plastic backing sheet to confine moisture within the moisture retaining layer. Such diapers are shown in U.S. Pat. Nos. 3,612,055 to Mesek et al. and in Re: 26,151 to Duncan et al.
The moisture retaining layer of prior art diapers have typically been comprised of a batt of loosely compacted cellulosic fibers. It has been known to provide such absorbent batts with an integrally formed densified paper-like layer or skin, and U.S. Pat. Nos. 3,017,304 to Burgeni and 3,612,055 to Mesek et al. are typical of such constructions. It is also known to provide absorbent batts having a continuous densified paper-like layer or skin with longitudinally extending thickened densified regions for directing moisture in a lengthwise direction of the batt, and Repke U.S. Pat. No. 3,938,522 is typical of such constructions.
It is also known to provide disposable diapers with reduced width crotch regions to reduce the bulk and provide improved fit and comfort. Such diapers are generally I-shaped, T-shaped or hour glass-shaped, and U.S. Pat. Nos. 3,559,648 to Mason, Jr. and 3,768,479 to Widland are typical of such constructions.
It is also known to provide absorbent batts for disposable diapers with increased liquid holding capacity in the central region of the batt, and heretofore this has been done by providing an extra batt layer (U.S. Pat. No. 3,612,055), depositing more absorbent material in the mid-portion of the batt (U.S. Pat. No. 3,938,522), or folding over the side marginal edges of the batt (U.S. Pat. No. 3,559,648). Such absorbent batts have had inadequate inherent structural integrity, and have not provided an adequate wicking mechanism for directing liquid away from an initially wetted area.
The use of so-called superabsorbent hydrocolloid materials in absorbent articles is also known for enhancing the absorbent capacity thereof. Materials of this nature are highly liquid-sorbent, and are capable of absorbing and retaining many times their own weight in liquid. While such materials are highly absorbent, incorporation of such materials in an absorbent article, such as a disposable diaper, can be problematic. Specifically, such superabsorbent materials generally do not act to efficiently wick or transport liquid, and thus, an associated wicking mechanism should be provided for promoting wicking of liquid throughout an absorbent product. In practice, such superabsorbent materials can actually prevent liquid-wicking, in that such materials can tend to coalesce and form a gelatinous mass when wetted which prevents wicking of liquid to unwetted portions of the material. This phenomenon is commonly referred to as "gel blocking", and can undesirably act to prevent effective and efficient use of the superabsorbent material by isolating liquid from unwetted portions of the material. While blends of particulate superabsorbent material and fibrous material such as wood pulp have been employed for enhancing absorptive capacity of an article (such as in U.S. Pat. No. 4,186,165, to Aberson et al.), it is believed that blending the absorptive materials in this manner can act to diminish the absorptive capacity of the fibrous material, since the superabsorbent swells and fills the void volumes of the fibrous material, which otherwise provide the liquid-holding capacity of the material. Poor wicking of liquid is also a problem in such superabsorbent/fibrous blends.
Furthermore, the very substantial swelling which takes place when such superabsorbent material absorbs liquid can undesirably impair the structural integrity or stability of an absorbent product into which such material is incorporated. Abating degradation of the structural integrity of an absorbent article having superabsorbent is particularly important since the article can be subjected to continued use after wetting (such as the case of a disposable diaper) with such integrity also facilitating handling and disposal of the article after use. Additionally, the texture of some superabsorbent materials after wetting can be objectionable, thus making it further desirable for the structural integrity of an absorbent article to be maintained after use so that the wetted superabsorbent is held in position within the article after use.
One manner in which superabsorbent material has been incorporated in an absorbent article is shown in U.S. Pat. No. 4,232,674, to Melican. This patent discloses deposition of superabsorbent material in a predetermined pattern, such as comprising parallel stripes, sandwiched between two layers of relatively non-absorbent tissue paper. The patent states that providing the pattern of superabsorbent in the form of stripes leaves channels between the stripes along and within which liquid can flow. While flow is stated as being primarily capillary to start with, larger channels are defined as the superabsorbent material swells, which diminishes flow caused by capillary action, since such capillary flow is promoted by close spacing of fibers of a fibrous material. It is further believed that this type of absorbent structure does not lend itself to maintaining the stability or structural integrity thereof attendant to swelling of the superabsorbent since it is specifically contemplated that the non-absorbent layers between which the superabsorbent is deposited are intended to be moved apart and separated during swelling of the superabsorbent. Further, it is believed that providing superabsorbent material between two tissue layers, in accordance with the teachings of this patent, does not address problems associated with the relatively large liquid volumes which must be absorbed and retained quickly by a disposable diaper. It is noted that this patent only discloses the embodiments of the tissue/superabsorbent construction in a sanitary napkin and tampon which generally need only absorb relatively small volumes of liquid at relatively small flow rates when compared to the desired characteristics of a disposable diaper.
U.S. Pat. No. 4,461,621, to Karami et al, also discloses an absorbent article which incorporates superabsorbent material. The article includes a backing sheet of fluid impervious material, and a fluid pervious cover sheet. A first absorbent pad comprising a loosely formed fibrous mass is provided adjacent the cover sheet, with either the upper or lower surface of the first pad coated with an absorbent polymer material. The article has a separate second absorbent pad intermediate the first pad and the backing sheet comprising a mass of fibers having a compressed region extending throughout a substantial part of the second pad. The polymer coating is described as extending at least a substantial part of the width of the pad and from the third to the sixth-tenth of the length of the pad. The patent discloses providing the polymer coating in two strips with a space therebetween to eliminate "gel block" at the central point of fluid excretion. As in other constructions, it is believed that the arrangement disclosed in this patent does not lend itself to maintaining the stability or structural integrity of the absorbent structure attendant to absorption and swelling of the polymer material, particularly when the polymer material is positioned on the surface of the first absorbent pad adjacent the second pad.
It would therefore be desirable to provide an absorbent unit for a disposable diaper, or the like, with increased liquid storage capacity in the central region thereof, while providing a wicking layer directly adjacent to the undersurface of the facing layer in contact with the infant's skin for rapidly directing liquid away from an initially wetted area. It would also be desirable to provide such a batt with a wicking mechanism whereby liquid spreading outwardly would be directed downwardly into lower portions of the batt remote from the layer in contact with the infant's skin. It would also be desirable to provide the mid-portion of such a batt with a strengthening means, so as to provide increased structural integrity, particularly when the diaper is to be worn for a prolonged period of time, such as overnight.
It would also be desirable to provide a disposable diaper having an absorbent unit incorporating highly liquid-sorbent superabsorbent material for enhanced liquid-holding capacity. Such a diaper should preferably be configured to promote wicking of liquid to all of the superabsorbent material provided therein, thus providing a high rate of liquid absorbency as is important in a disposable diaper.